Fate modelling of nanoparticle releases in LCA: An integrative approach towards “USEtox4Nano”

Abstract

The aim of this paper is to present a new, integrative approach for calculating Fate Factors (FF) for nanomaterials by combining the USEtox2.0 modelling framework with SimpleBox4Nano (SB4N), an advanced environmental fate model for nanomaterials, and to demonstrate its application to life cycle assessment (LCA) by the estimation of characterisation factor (CF) for nano-TiO2 for the impact category of freshwater ecotoxcity. To enable the combination of the USEtox model with SB4N, two principle adaptations were made: (i) the compartments of air and rain were merged, and (ii) the sum of the free, aggregated, and attached species was accounted for in the receiving compartments. Furthermore, a dynamic analysis was conducted to characterize the dynamic behaviour of nanoparticles and to estimate the time at which steady state is actually reached. Our combined USEtox-SB4N approach was then applied to calculate i) the Fate Factor (FF) for unitary emissions of nano-TiO2 to air, freshwater, soil and sediment, and ii) using these, characterisation factors (CF) for nano-TiO2 in the case of the impact category freshwater ecotoxicity. The FF for unitary emissions of nano-TiO2 as free species was calculated. Persistence was found to be highest for emissions to soil (FFs,s = 2.9·105 days), followed by emissions to water (FFw,w = 128 days) and, then for an emissions to air (FFa,a = 3.3 days). The results of the dynamic analysis showed that the soil compartment in fact behaves as a storage compartment. Finally, an update of the freshwater ecotoxicity CF for nano-TiO2 was calculated (CF = 3443 PAF day m3 kg−1), based on the here established FF. The integrative approach presented here for calculating nano-specific FF values serves to reduce the complexity of the S4BN model and make the USEtox modelling framework fit for use with nanomaterials. This approach can be seen as a first step towards a “USEtox4Nano” characterisation model.